Electron discharge apparatus



y z km w E 0 N0 2 E@ 5, www 2 1s Y W s. w L mw m M f D Mmm /yf 4m mmm.. MM G @uw I. wn 2 .Dd 0# smh @M5 C m E Aug. 29, 1950 ATTORNEY Patented Aug. 29, 1950 ELEoTRoN DISCHARGE APPARATUS Stanley Gordon Tomlin, London, England, as-

signor, by mesne assignments, to International Standard Electric Corporation, New York, N. Y., a corporation of Delaware Application September 18, 1942, Serial No. 458,806 In Great Britain December 24, 1940 Section 1, Public Law 690, August 8, 1946 Patent expires December 24, 1960 This invention relates to electron discharge apparatus utilising the principles of electron velocity modulation and consists in a modification of the invention claimed in United States patent application Serial No. 457,800 filed September 9, 1942, now Patent No. 2,421,043.

The present invention consists in a frequency changing apparatus for very high frequencies employing the principles of electron velocity modulation comprising a tube including an electrode system for generating an electron `beam and directing it through gaps in a high frequency resonator, a grid electrode and a collector electrode in the path of the beam and means for maintaining the electrodes at such potentials that the operating condition of the tube is at a curved part of the grid-voltage collector-current characteristic, in which by adjustment of the beam velocity the device is caused to generate oscillations at a frequency slightly different from that of the source of applied waves, whereby the collector electrode current has an intermediate frequency component.

Another feature of the invention consists. in a frequency changing apparatus for very high frequencies employing the principles of electron velocity modulation comprising a tube including an electrode system for generating an electron beam and directing it through gaps in a high frequency resonator, a collector electrode, means for maintaining the electrodes at such potentials that the operating condition of the tube is at a curved part of the collector-current collectorvoltage characteristic, in which by adjustment of the beam velocity the device is caused to generate oscillations at a frequency slightly dierent from that of the applied waves, whereby the collector electrode current has an intermediate frequency component.

In carrying out the invention, similar apparatus to that described in the said prior application is employed.

The above mentioned and further objects and advantages of the invention and the manner of attaining them will be more fully set forth in the following description taken in conjunction with the accompanying drawings in which Fig. 1 is a longitudinal section, partly diagrammatic of an electron discharge device in accordance with my invention Fig. 2 is a diagrammatic cross-section of the device shown in Fig. 1 and Fig. 3 is a curve illustrating the operation of the device.

Referring to the gures coaxial conductors I and 2 form a resonator of adjustable length, a coaxial line 3, 4 terminating in a loop 5 serves to feed incoming waves to the resonator. A cathode or electron gun 6 projects a beam of electrons past focussing and accelerating electrodes 1, 8 through apertures 9, l0 in the conductors l' and 2 at the point of a voltage anti-node. Fins Il are provided to reduce the gaps between the conductors at the apertures. The electrons are modulated in velocity in passing the gaps between the conductors. Beyond the resonator, and in the path of the beam, is a wire mesh grid l`2 maintained at a relatively low potential approximately cathode potential and a collecting electrode I 3 maintained at a suitable potential positive with respect to the cathode. The resonator is designed so that the gaps A and B between the inner and outer conductors are small in order that the transit time across a gap is small compared with a period of an oscillation of the applied waves and the diameter of the inner conductor is such that the transit time of electrons in moving from the centre of the iirst gap to the centre of the second gap is an odd number of half periods of the applied frequency.

If the transit time of electrons travelling from the resonator to the grid electrode is suitably adjusted, owing to the reflection of electrons from the low potential grid electrode, the valve will generate oscillations. For a given apparatus, the frequency of oscillation may be varied by adjustment of the resonator tuning and of the beam velocity, the latter regulating the electron transit times.

Now .assuming that the resonator is tuned to resonate at the frequency (W1) which it is desired to receive7 and the apparatus is caused by adjustment of the beam velocity to generate oscillations at a frequency (W2) slightly different from that of the received waves, then the voltage existing across the gaps A and B in the resonator may be represented by:

VA sin Wit-l-VB sin Wzt (1) Thus electrons passing through the resonator will be velocity modulated by a potential of this form and a graph showing the modulation velocity would be a beat frequency curve.

The intermediate frequency is detected by a frequency component detector i4 coupled to the collector electrode I3.

The production of an intermediate frequency from such a beam of electrons depends upon the grid-voltage collector-current characteristic. This curve is of the form shown in Fig. 3 where 3 the collector current is plotted against the static potential of the grid. We may regard the grid voltage changes as equivalent to velocity variations of the'eleetronxbeam, at leastin arstiape proximation,` and thus We see that "the'collectore 5 current is a non-linear function of the velocity modulation of the beam. Hence, when the bearn` is modulated by a potential of theformaoflthel. Equation 1 the collector current will have a component of the form: y

I=Io Sin (Wi-Wzli (2),v

i. e. the collector current has an intermediate'- frequency component whichnmaybeefedsintou a standard intermediate frequency .ampliernfol-.- l5

lowed by a detector and of necessaryaudio fre- 'quency output stages.

and. the .-colleetor-f,` electrode is :maintained-.at 'Lap-- proxirnately,,cathodef potential.; 'It the spacing of, lthe.- colieetor. velectrode-.andv the potentials-.applied fto; the r eleetrodes.- are? suitablychosen f the tube may ,-beicaused 'to-` generate osciliations'of-.Ia frequencyslightly different from thateof-ttlrie-apl pliedf,W-aves.y In this case the-tubeis arranged to Y operatenon arcuvvedfpart :ot ;tl'le.colleetor-currentv colleetorfvoltage characteristie;` and .tlflewoollector current =,\vil1ha.ve..anintermediatefrequency'-come ponent.-.

What .isflolaimed-vlis: y

l?. A frequency changing;device-comprisinggan: electron; discharge tubef including@ a nigh 1 requencyxresonatointunedto incoming waves,- electron-:beam generating means positionedY adjacent said-rresonator,to .projeet-a beam of electronslin, afpath through zsaidrvresonator, means -coupledftow said resonator'` for lapplyinglthe-incoming Waves, a.Y

collecting electrode@ positionedLl in the:l path i ctr 45 saidl :.beamadjaeent .said-resonator1 for collecting electrons from saidbeamf means -ceupledto saidl electrode.- fory applying.-biasingpotential thereto. afreiiecting .electrode mounted between'said resonator and said collecting electrode and positioned at a distance from said resonator providing an electron transit time from said resonator tossaidirefiectingselectrode esuch' ythat :electrons reiiectedtherefrom` causefsaid resonator -fto oscillate at a frequency slightly different from the -frequency of the incoming Waves whereby renec-.ted .electrons cause said resonator to oscillate at said slightly different frequency, and output *means coupled tofsaid .collecting electrode for detectinglthe frequency component of said electrode current-'whichis'thebeat frequency between the fr'equency'of'th'eincoming waves and that of the oscillating gresonator.l

211Afrequerrcy changing apparatus according to claim. 1 in.which said resonator comprises a coaxialline'provided with diametric apertures in the inner and `outer conductors at a eld antinode :through which apertures the electron beam is adapted to be projected, the length of said coaxial, line beingffadjustablefto. tune` the `resonator to.thelapplied .highfrequency Waves.-

STANLEY; GORDON .TOMLIN REEERENCE S :CIT EIT The following. :referencesrare .of record: in .the'

leeoffthis patent:

UNITED STATES PATENTS;

Journal .of 'AppliedPlysics vol.: 10, No. li,lMay, 

